Surface plate coatings



Patented Oct. 16, 1945 UNITED STATES PATENT OFFICE v I SURFACE i 'fljzoATmGs I Arthur w. Buck and Joseph w. Miller, St. Louis, Mo., assignors to Buck X-Ograph Company, St. Louis, Mo., a corporation of Missouri No Drawing. Application April 12, 1943,

Serial No. 482,824

, 2 Claims.

This invention relates to a dichromate surface plate'coating for use in the lithographic conditions.

' The present invention has for an object to provide a coating eliminating the use of albumen and which assure long and uniform press runs and also rendering high negative values, smoother tints and finer detail than ordinarily obtained byuseofegg albumen. h

It is also an object or the invention to provide a dichromate surface plate coating solution by dissolving into a single solution a correctly proportioned combination of casein and gelatin, plus an alkali, to which solution a proper amount of ammonium dichromate is added.

The use of dichromated gelatin has long been known to the industry but its water absorption characteristic in connection with its excessive ink While particular reference is made to borax, it is stated that other alkali in varying amounts will produce satisfactory results.

The relative amounts of casein and gelatin hereinbefore mentioned have-been found to produce desirable results but we do not wish to be limited to this exact proportion as an increase or decrease of the amounts hereinbefore stated might be used with varyin success under certain conditions. However, the use of less than four parts of gelatin to twelve parts of casein has been found to produce a coating which is too hard and lacking in flowability while more than six parts of gelatin to twelve parts or casein have been found to .be too soft and water abscrbent.

absorption, noticeably reduces its sharpness oi.

metallic plates. It is a purpose of the invention to provide a coating free of these objectionable features.

The present invention comprises a solution in cluding:

Parts Garcia 12 Gelatin 5 Alkali (hos-ax) 1 In preparing the solutien, the casein, gelatin and alkali, which is in powdered form, are added to the usual sensitizer, such as now employed in egg albumen, and which usually consists of water 32 oz. and ammonium dichromate approximately 1 V oz.

The coating or solution as embodied in the present invention is applied in accordance with the method now well known to the industry and is the same in principle as that now employed with the use of egg albumen.

What is: claimed is:

1. A solution for coating a printing plate comprising, asensitizer, casein approximately 12 parts, gelatin from 4 to 6 parts, and box-ax approximatelyl part.

2. A compositionv for addition toga sensitizer solution for use as a printing plate coating. cOn- ARTHUR W. BUCK. JOSEPH W. MILLER. 

